Yangtze-Huaihe River Research Articles

Stratospheric Quasi‐Biennial Oscillation Modulates the Impact of Boreal Summer Intraseasonal Oscillation on Rainfall Extremes in the Yangtze–Huaihe River Basin

AbstractThe impact of the boreal summer intraseasonal oscillation (BSISO) on rainfall anomalies in the Yangtze–Huaihe River Basin (YHRB) was found to be modulated by the stratospheric quasi‐biennial oscillation (QBO), which is reasonable for the close associations between the QBO and summer extreme precipitation in the YHRB. It was found that the extreme precipitation preferentially occurred in the YHRB during the easterly phase of the QBO (EQBO) compared to the westerly phase of the QBO (WQBO). This was primarily because the BSISO was more prone to cause rainfall extremes in the YHRB during the EQBO summers than during the WQBO summers. The EQBO can induce the background stratospheric easterly wind to arch downward into the troposphere, which enhanced the BSISO‐associated moisture transport and moisture convergence and thus resulted in stronger rainfall extremes in the YHRB.

Restore polder and aquaculture enclosure to the lake: Balancing environmental protection and economic growth for sustainable development

The restoration of lakes and their buffer zones is crucial for understanding the intricate interplay between human activities and natural ecosystems resulting from the implementation of environmental policies. In this study, we investigated the ecological restoration of shallow lakes and buffer zones in the Yangtze-Huaihe River Basin, specifically focusing on the removal of polder and aquaculture enclosure areas within the lakes. By examining data from eight shallow lakes and their corresponding buffer zones, encompassing lake morphology, water quality parameters, and land use/land cover (LULC) data spanning from 2008 to 2022, which shed light on the complex relationships involved. During the process of restoring polder and aquaculture enclosure areas, we observed a general decrease in the extent of polders and aquaculture enclosures within the lakes. Notably, the removal of aquaculture enclosures had a more pronounced effect (reduction rate of 83.37 %) compared to the withdrawal of polders (reduction rate of 48.76 %). Linear regression analysis revealed a significant decrease in the concentrations of seven water quality parameters, including COD, CODMn, TN, TP, NH3-N, Chl-a, and F, while pH and DO factors exhibit a distinct increasing trend. The results of redundancy analysis and Pearson correlation analysis demonstrated significant correlations between the area of polders and aquaculture enclosures and the changes in lake water quality. Encouragingly, the withdrawal of polders and the removal of aquaculture enclosures had a positive impact on the lake water quality improvement. In contrast, the LULC in the buffer zones of the lakes experienced a gradual decline owing to land degradation, resulting in a reduction in ecosystem service value (ESV). These results offer valuable support for policymakers in their endeavors to restore lake water quality, mitigate the degradation of buffer zones land, and promote the sustainable development of land and water resources.

Comparative analysis of peak-summer heatwaves in the Yangtze–Huaihe River Basin of China in 2022 and 2013: Thermal effects of the Tibetan Plateau

In the peak-summer of 2022, the Yangtze–Huaihe River Basin (YHRB) in China experienced its most extreme heatwaves since 1961. Notably, a rare heatwave also occurred in the YHRB in 2013. However, the Tibetan Plateau (TP) exhibited different thermal conditions during those two years. Observational analysis indicates that the 2013 and 2022 heatwaves were closely related to the local anomalous high pressure. The synergistic effects of the East Asian subtropical jet (EASJ), South Asian high (SAH), western Pacific subtropical high (WPSH), and divergence of moisture, supported the formation and maintenance of the high pressure. Compared to 2013, under the synergistic control of these intensified circulation systems in 2022, which led a broader descending motion and stronger heatwaves prevailed over the YHRB. Also, the surface air temperature of TP reached its highest value in 2022, whereas it was not distinctly anomalous in 2013. Corresponding to the TP thermal anomaly, an abnormal high pressure appeared throughout the troposphere over the northern YHRB. The TP heating contributed to the northward strengthening of the SAH and EASJ, which enhanced the anomalous westerly winds to the north of the anticyclone. Moreover, the WPSH extends westward during strong TP heating years. With the cooperation of high pressure and moisture, there was an anomalous meridional circulation pattern with ascending motion in North China and descending motion in the YHRB, accompanied by reduced cloud cover and increased insolation in the YHRB, leading to further intensification of local heatwaves in 2022. This study demonstrates the significant role of TP thermal anomaly in YHRB heatwaves.

Characteristics of Warm‐Season Mesoscale Convective Systems Over the Yangtze–Huaihe River Basin (YHR): Comparison Between Radar and Satellite

AbstractMesoscale convective systems (MCSs) are crucial in modifying the water cycle and frequently induce high‐impact weather events over eastern China. Radar and Climate Prediction Center (CPC)‐4 km satellite‐derived infrared cloud top temperature (Tb) data were used to thoroughly analyze the long‐term climatology of MCSs over eastern China, particularly in the Yangtze–Huaihe River Basin (YHR) in the warm season from 2013 to 2018. For the first time, we contrasted the effects of data set selection and threshold setting on research outcomes. The large‐scale environments of MCSs initiation were also investigated using the latest global reanalysis data ERA5. It is found that striction of thresholds, including duration, reflectivity/Tb, area, and linearity, would lead to a greater proportion of early‐morning MCSs. Satellite‐identified MCSs differed from radar‐derived ones, exhibiting afternoon diurnal peaks, faster movement speeds, longer travel distances, and expansive impact areas. The center of MCS and related precipitation shifted northward from Pre‐Meiyu to Post‐Meiyu seasons, contributing to up to 20% of total rainfall, with most MCSs moving along eastward trajectories. MCSs typically had the most substantial impact in the Meiyu season because of the most prolonged duration, largest convective core area, and strongest precipitation intensity. Warm‐season MCSs initiated ahead of midlevel troughs and were related to strong anomalous low‐level convergence and midlevel upward. The circulation anomalies were the strongest in the Pre‐Meiyu season among the three subseasons, with most moisture sourced from the southwest.

Precipitation, microphysical and environmental characteristics for shallow and deep clouds over Yangtze-Huaihe River Basin

The precipitation, microphysical, and environmental characteristics of shallow and deep precipitation clouds (SPCs and DPCs) are investigated over the Yangtze-Huaihe River during the summers from 2014 to 2021, using the observational data from dual-frequency precipitation radar (DPR) on board Global Precipitation Mission and the reanalysis data. DPCs (SPCs) are mainly associated with convective (stratiform) precipitation, contributing approximately 2% ∼ 15% (20% ∼ 40%) to the total precipitation events, while contributing only around 0.05–0.15% (below 0.05%) to the total rainfall. Compared to SPCs, the rain hydrometeors for DPCs are mainly composed of lower concentrations of larger-sized hydrometeors near the surface, showing larger mass-weighted mean diameter (Dm: 1.0 to 3.0 mm) and lower generalized intercept parameter (Nw: 20 to 40 dBNw) at 2 km in altitude. Below the melting layer, the Dm, reflectivity, and rain rate of DPCs decrease rapidly as the decreasing altitude, reflecting the breakup or the evaporation of liquid hydrometeors, while those of SPCs rapidly increase, indicating vigorous processes of collision and coalescence. DPCs tend to occur in environmental conditions with increased convective available potential energy (CAPE) and higher surface air temperatures, but drier low-level humidity, compared to SPCs. Furthermore, the DPCs tend to occur in the environment with more significant updraft (≥5 m s−1) in comparison with SPCs. Especially at 4 km and 10 km in altitude, the updraft fractions could reach 45% and 38%, respectively. These results may provide an observational reference for the microphysical parameterization in numeric models for the vertical development of storms.

Short-term forecast large-scale error characteristics and their relationship with precipitation forecast skill under two rainfall regimes

Although precipitation forecast skill has improved significantly in recent decades, both location and intensity of precipitation forecast based on kilometric-scale numerical weather prediction (NWP) models still contain errors. The importance of large-scale error in NWP has been recognized, but characteristics of large-scale error under different rainfall regimes and the influence of large-scale error on precipitation forecast skill remain unclear. In this regard, we focused on the Yangtze-Huaihe River Basin (YHRB) and used an operational forecast dataset covering the summer seasons of 2018 and 2019 obtained from the Anhui Meteorology Observatory to investigate large-scale error characteristics and their relationship with precipitation errors under two rainfall regimes.Large-scale error characteristics were measured by root-mean-square errors (RMSE), relative RMSE (RRMSE), and large-scale spatial pattern correlation (LSCC). The large-scale RMSEs were highly correlated with the rainfall intensity and area, while the large-scale RRMSE and LSCC can be used to describe precipitation forecast skill for rainfall events under the two rainfall regimes. In general, the precipitation forecast for strongly forced rainfall events performed better than that for weakly forced rainfall events. Under strong forcing conditions, the majority of rainfall events were concentrated in the intervals of smaller precipitation errors with smaller RRMSEs and higher LSCCs, and the precipitation forecast skill was weakly related to the large-scale RRMSE, LSCC and the initial large-scale variance contribution (LVC). Under weak forcing conditions, most of the rainfall events had a larger precipitation error and the frequency of location error was higher than that of intensity error. The low precipitation forecast skill and large forecast uncertainties for weakly forced rainfall events were strongly related to the large RRMSEs and low LSCCs in the geopotential height in the middle-upper troposphere and meridional wind component (V) in the lower troposphere. In particular, a strong negative correlation was found between the initial LVC and the large-scale RRMSE under weak forcing. This suggests that large-scale information could play a more important role in precipitation forecast for weakly forced rainfall events, and could potentially be used to indicate the magnitude of large-scale forecast errors in short-term forecasts under weak forcing conditions.

Vertical profiles and regional transport of ozone in typical area of Yangtze-Huaihe River Basin during the autumn base on multiple lidars

In recent years, the Yangtze-Huaihe River Basin has become one of the key areas of air pollution control in China, however, there are some differences in the spatial and temporal characteristics of ozone in different cities. In order to explore the vertical structure characteristics of ozone in Yangtze-Huaihe River Basin and its influencing factors, this study analyzed the vertical and horizontal distribution of ozone in typical cities in the Yangtze-Huaihe River Basin in October 2021 by using differential absorption lidar(DIAL), temperature and humidity profile lidar and wind profile radar system, studied two typical ozone pollution processes, and the meteorological factors of ozone pollution at vertical height. The results showed that the ozone pollution was mainly produced locally from October 13 to 14, while the ozone pollution was affected by local production and transport from October 21 to 31, the average ozone concentration reached a maximum of 357.6 μg/m3. There is a significant residual layer at night. The temperature of 272.85–285.88 k and water vapor mixing ratio of 3.22–5.7 g/kg are favorable for ozone generation in Huaibei City. The ozone contribution of Henan, Shandong and Anhui to Huaibei City is above 200 μg/m3. The study on the vertical structure of ozone is helpful to fill the knowledge gap between the evolution of ozone events in Yangtze-Huaihe River Basin.

Potential causes of megapluvials in the Yangtze–Huaihe River valley over the last millennium

The potential causes of megapluvials over Yangtze–Huaihe River valley (YHRV) during the last millennium were investigated using the Community Earth System Model-Last Millennium Ensemble (CESM-LME) simulation data and multiple proxy data (i.e., reconstruction and paleoclimate assimilation data). Herein, we first depicted the spatial hydroclimatic pattern over the Northern Hemisphere when megapluvials occurred in the YHRV during the last millennium. The proxy and simulation data both showed that megapluvials in YHRV were accompanied by extensive decadal drought in western Asia and northwestern India, also located in mid to low latitudes. Then, by diagnosing the dynamic processes, we found that the baroclinic structure over western Asia and northwestern India caused anomalous geopotential heights, and hence triggered the negative phase of the Circumglobal Teleconnection (CGT). The eastwards wave train at mid-latitudes disturbed by the CGT mode, triggered lower-level northerlies and upper-level southerlies over the northern part of the YHRV and, as a consequence, led to anomalous strong convection near the YHRV. Together with abundant water vapour from the Pacific Northwest, there was a synergistic effect on megapluvial events over the YHRV. Finally, we analysed the linkage of surface temperature in western Asia and northwestern India and megapluvials in the YHRV. Land surface heating over western Asia and northwestern India may largely stimulate the formation of a negative CGT mode through local feedback of air–land interactions and, as a result, affect precipitation anomalies downstream, such as in the YHRV. It is therefore necessary to consider anomalous high surface temperatures in western Asia and northwestern India as important predictors for interdecadal severe floods in the YHRV.

To what extent can the ozone valley over the Tibetan Plateau influence the East Asian summer precipitation?

The ozone valley over the Tibetan Plateau (OVTP) has experienced significant interannual variations during the past decades. Previous studies have primarily focused on the origins of OVTP rather than its climate impact. This study reveals that OVTP during its peak season (May–July) explains up to 15% of the summer precipitation variability in East Asia. The results suggest that the surface temperature (Ts) anomaly over the Tibetan Plateau (TP) acts as a link between OVTP and East Asian precipitation. Through the positive land-atmosphere feedback, the Ts anomaly over the TP is amplified. The anomalous Ts pattern persists into summer (June–August) due to the land memory effect and impacts the East Asian precipitation by modulating the local circulation. The Specified-Chemistry version of the Whole Atmosphere Community Climate Model is employed to validate that MJJ OVTP results in a substantial increase of Ts over TP and induces an anomalous anti-cyclone centered over the Yangtze-Huaihe River Basin during summer. Consequently, negative precipitation anomalies are observed in the Yangtze River Basin, while positive precipitation anomalies occur in Southern China. The linear baroclinic model further demonstrates that the diabatic heating over the TP serves as the link between MJJ OVTP and East Asian summer precipitation patterns. Our analysis of Coupled Model Intercomparison Project Phase 6 models reveals that a more accurate prediction of East Asian precipitation requires an improved understanding of the relationship between OVTP and TP Ts.

The Quadrupole Precipitation Pattern over Eastern China and Its Associated Atmospheric Circulations and Ocean Conditions

Abstract The diversity of summer precipitation regimes over eastern China has raised concerns. Its variations during different warming periods and the relevant mechanisms remain unclear. In this study, the decadal precipitation changes and the associated atmospheric circulations, ocean conditions, and warming over Northern Hemisphere were investigated. The results indicated a quadrupole precipitation pattern over eastern China in the boreal summer, with a significant shift around 1998. From 1985–98 to 1999–2014, two wet anomalies were over North China (NC) and South China (SC), while two dry anomalies were over the Yangtze–Huaihe River basin (YHRB) and northeastern China (NEC). This quadrupole pattern is associated with the circumglobal teleconnection (CGT), the negative phase of the interdecadal Pacific oscillation (“−IPO”), the warming over the high latitudes of North Atlantic (“+HNA”), and the warming rate over the Northern Hemisphere (NWR). The CGT would induce the weakened polar front jet (PJ), southward shift of the PJ, and northward shift of the entire subtropical jet (SJ), which decreased the meridional distance between the PJ and SJ, and therefore resulted in the NC-wet–YHRB-dry–SC-wet variation. As well, the dry NEC was attributed to the enhanced PJ, weakened Iranian Plateau subtropical jet (IPSJ), and northward movement of the PJ and Tibetan Plateau subtropical jet (TPSJ), which were accompanied by −IPO and +HNA. Moreover, the NWR led to the weakened PJ and SJ, as well as the southward shift of PJ, also contributed to the dry YHRB, and wet anomalies over NC and SC. Particularly, the +HNA plays an important role in this quadrupole precipitation variation. Our findings have highlighted the role of jet streams in complex precipitation patterns, which will contribute to understanding the diverse variations in precipitation regimes over eastern China under global warming. Significance Statement The purpose of this study is to understand the regime shifts of the East Asian summer monsoon precipitation in different warming periods. We revealed a new precipitation pattern over eastern China as a “+ − + −” precipitation pattern from south to north. The circumglobal teleconnection, the negative phase of the interdecadal Pacific oscillation, the warming over the high-latitude North Atlantic, and the warming over Northern Hemisphere can be used to explain the quadrupole precipitation pattern. These findings could highlight the role of jet streams linking the quadrupole pattern to the teleconnections, dominant decadal ocean variabilities and the warming over Northern Hemisphere. Future work will focus on the role of Arctic rapid warming in summer precipitation over eastern China.

Relationships between environmental factors and N-cycling microbes reveal the indirect effect of further eutrophication on denitrification and DNRA in shallow lakes

Traditional views indicate that eutrophication and subsequent algal blooms favor denitrification and dissimilatory nitrate reduction to ammonium (DNRA) in lake ecosystems. However, lakes tend to show an increasing propensity for inorganic nitrogen (N) limitation as they become more eutrophic. Thus, the influence of further eutrophication on denitrification and DNRA in eutrophic lakes are unclear due to the uncertainty of N availability. To fill this gap, we investigated the genes abundance (AOA, AOB, nirS, nirK and nrfA) and the composition of N-cycling microbes through quantitative PCR and 16S rRNA sequencing analysis, respectively, in 15 shallow eutrophic lakes of the Yangtze-Huaihe River basin, China. The results indicated that denitrification and DNRA rates could be modulated mainly by their functional gene abundances (nirS, nirK and nrfA), followed by the environmental factors (sediment total organic carbon and nitrogen). Denitrification rates significantly increased from slightly to highly eutrophic lakes, but DNRA rates were not. An explanation is that nitrification provided ample nitrate for denitrification, and this cooperative interaction was indicated by the positive correlation of their gene abundances. In addition, Pseudomonas and Anaeromyxobacter was the dominant genus mediated denitrification and DNRA, showing the potential to perform facultative anaerobic and strict anaerobic nitrate reduction, respectively. High level of dissolved oxygen might favor the facultatively aerobic denitrifiers over the obligately anaerobic fermentative DNRA bacteria in these shallow lakes. Chlorophyll a had a weak but positive effect on the gene abundances for nitrification (AOA and AOB). Further eutrophication had an indirect effect on denitrification and DNRA rates through modulating the genes abundances of N-cycling microbes.

Characteristics of Warm-season Mesoscale Convective Systems over the Yangtze-Huaihe River Basin (YHR)––comparison between radar and satellite

Characteristics of Warm-season Mesoscale Convective Systems over the Yangtze-Huaihe River Basin (YHR)––comparison between radar and satellite

Typhoon-related changes in moisture pathways and sources for precipitation in Eastern China during the three major rainy seasons

Typhoons (TYs) and their interactions with large-scale ambient flow might exert an important control on moisture transport and precipitation. In this study, we used a Lagrangian model, the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT), to quantify changes in moisture pathways and sources associated with TY activity in relation to precipitation in eastern China during the three major rainy seasons. We compared TY-active and TY-inactive periods, i.e., the periods with and without TYs (maximum sustained surface wind speeds of up to 32.7 m/s), over the western North Pacific (WNP) to investigate TY-associated changes for the period 1979–2020. During the pre-summer rainy season in South China, anomalous moisture exhibited a north–south dipole pattern, with moisture contributions from the region extending from the South China Sea to the adjacent tropical WNP showing a 17.0% decrease during TY-active compared with TY-inactive periods (34.7% versus 41.8%, respectively), and contributions from the region extending from southwestern China to the northwestern North Pacific showing a 18.9% increase (17.0% versus 14.3%, respectively) and those from the Bay of Bengal showing a 16.6% increase (17.6% versus 15.1%, respectively). The moisture anomaly during the Meiyu rainy season in the Yangtze–Huaihe River Basin had an east–west dipole structure, with the moisture contribution from the Bay of Bengal reduced by 21.8% as compared with TY-inactive periods, and that from the WNP increased by 62.3%. During the rainy season of North China, the moisture contribution from the Indian Ocean decreased by 7.2%, while that from the WNP increased by 8.7% and from Northeast China increased by 10.0%. In addition, during TY-active periods, moisture contributions with local origins showed a slight increase.

Heavy Metal Concentration, Source, and Pollution Assessment in Topsoil of Chuzhou City

In order to understand the pollution level and ecological risk of heavy metals in topsoil of Chuzhou City, a total of 4360 soil samples in Chuzhou City were collected, and the concentrations of eight heavy metals including Cr, Zn, Pb, Cu, Ni, Cd, As, and Hg were measured. Correlation analysis, cluster analysis, and principal component analysis were used to analyze the sources of the heavy metals, and the enrichment factor index, single-factor pollution index, pollution load index, geo-accumulation index method, and potential ecological risk index were selected to assess the environmental risk of the eight heavy metals in the topsoil. The results showed that the average values of Cr, Zn, Pb, Cu, Ni, Cd, As, and Hg contents in the surface soil of Chuzhou City were higher than the background value of that in the soil of Yangtze-Huaihe River Basin of Anhui, and Cd, Ni, As, and Hg were significantly different in space and influenced by external disturbance. The eight types of heavy metals could be divided into four categories based on correlation analysis, cluster analysis, and principal component analysis. Cr, Zn, Cu, and Ni were from natural background sources; As and Hg mainly came from sources of industrial and agricultural pollution; Pb mainly came from the sources of transportation pollution and industrial and agricultural pollution; and Cd came from the sources of transportation pollution, natural background, and industrial and agricultural pollution. The overall pollution degree of Chuzhou City was low, and the ecological risk level was at a slight level based on the pollution load index and the potential ecological risk index; however, the ecological risk of Cd and Hg was generally serious, and these two heavy metals should be taken as the objects of priority control. The results provided a scientific basis for soil safety utilization and classification control in Chuzhou City.

The record-breaking 2022 long-lasting marine heatwaves in the East China Sea

In 2022, record-breaking long-lasting marine heatwaves (MHWs) occurred in the East China Sea (ECS), which persisted for 62 d during boreal summer. This exceeded the average MHWs duration of 10 d by a factor of 6. In addition, 2022 was also recorded as a year of many extreme events throughout Asia, such as summer floods in China and Pakistan, droughts and extreme heat in Europe, raising the question of whether they were caused by a ‘triple-dip’ La Niña, which has persisted since September 2020. Here we examine the key local and remote processes that led to the 2022 MHWs in the ECS using mixed-layer heat budget analysis. During the onset of the MHWs, a salinity-stratified shallow mixed-layer due to the large river discharge from the Yangtze–Huaihe River floods in June created favorable conditions for warm ocean temperature in the ECS. Simultaneously, an anomalous anticyclone maintained by the stationary Rossby wave, which is generated by vorticity forcings in mid-latitudes and thermal forcing in Pakistan, settled in the corresponding region and led to the long-lasting MHWs until Typhoon Hinnamnor began to dissipate the wave in early September. This study improves our understanding of the physical mechanism of flood-related MHWs that have increased with recent climate change.

MPAS‐A Variable‐Resolution Simulations for Summer Monsoon Over China: Comparison Between Global and Regional Configuration

AbstractDriven by ERA‐Interim reanalysis, two climate simulations are conducted from April to August for 20 years (1998–2017) during the East Asia summer monsoon with Model for Prediction Across Scale‐Atmosphere (MPAS‐A). The global variable‐resolution (MPAS‐VR) and regional (MPAS‐RCM) configurations are adopted under the same model framework with 92–25 km mesh refinement centered over Mainland China (MPAS‐A experiments hereafter). MPAS‐VR allows flexible interactions across scales. Constrained by the “reanalysis‐based” lateral boundary conditions (LBCs), MPAS‐RCM could well capture the evolution of large‐scale fields and becomes a proper reference for evaluating MPAS‐VR. The evaluations are conducted for precipitation, near‐surface air temperature, and circulation features against observed climate. Two MPAS‐A experiments present comparable results for the mean climatology and interannual variability except that MPAS‐VR presents wet biases along the tropical ocean and underestimation in the Yangtze–Huaihe River basin. Compared with MPAS‐VR, MPAS‐RCM presents better daily variations and rain belts’ evolution, which demonstrates the crucial effects of the LBCs for the limited‐area model. The simulated circulation and moisture flux can explain most of the deviations. However, two MPAS‐A experiments show consistent results for the extreme precipitation frequency and the extreme indices over Mainland China. With the same dynamic core and model physics, those climate features are similarly resolved by the two simulations. Thus, the 92–25 km MPAS‐VR simulation is demonstrated as a promising tool for regional climate hindcast.

Performance of Seven Land Surface Schemes in the WRFv4.3 Model for Simulating Precipitation in the Record-Breaking Meiyu Season Over the Yangtze-Huaihe River Valley in China.

In 2020, the Yangtze-Huai river valley (YHRV) experienced the highest record-breaking Meiyu season since 1961, which was mainly characterized by the longest duration of precipitation lasting from early-June to mid-July, with frequent heavy rainstorms that caused severe flooding and deaths in China. Many studies have investigated the causes of this Meiyu season and its evolution, but the accuracy of precipitation simulations has received little attention. It is important to provide more accurate precipitation forecasts to help prevent and reduce flood disasters, thereby facilitating the maintenance of a healthy and sustainable earth ecosystem. In this study, we determined the optimal scheme among seven land surface model (LSMs) schemes in the Weather Research and Forecasting model for simulating the precipitation in the Meiyu season during 2020 over the YHRV region. We also investigated the mechanisms in the different LSMs that might affect precipitation simulations in terms of water and energy cycling. The results showed that the simulated amounts of precipitation were higher under all LSMs than the observations. The main differences occurred in rainstorm areas (>12mm/day), and the differences in low rainfall areas were not significant (<8mm/day). Among all of the LSMs, the Simplified Simple Biosphere (SSiB) model obtained the best performance, with the lowest root mean square error and the highest correlation. The SSiB model even outperformed the Bayesian model averaging result. Finally, some factors responsible for the differences modeling results were investigated to understand the related physical mechanism.

Extreme precipitation driven by the rapid tropical Atlantic warming and the second developing La Niña over the Yangtze–Huaihe River Basin in August 2021

Extreme precipitation driven by the rapid tropical Atlantic warming and the second developing La Niña over the Yangtze–Huaihe River Basin in August 2021

Evolution characteristics of impact weather system and SST signals during years of anomalous Meiyu onset over the Yangtze-Huaihe River Basin

This article investigates the climatic characteristics of Meiyu over the Yangtze-Huaihe River Basin and the primary impact system based on Meiyu onset data from 1954 to 2020, precipitation during the Meiyu Period, NCEP/NCAR reanalysis data, sea surface temperature (SST) data of NOAA, and western Pacific subtropical high (sub-high) data provided by the National Climate Center. The main analytical method used is synthetic analysis. The results indicate that the Meiyu onset date has enormous interannual variation. The date of the earliest Meiyu emergence is 27 days prior to the latest. There is a strong relationship between the duration of Meiyu and rainfall. The start of Meiyu correlates with the northward motion of the South Asia High, the northward jump of the westerly jet, the northward jump of the subtropical high, and the northward motion of the low-level jet. In the early Meiyu years featured in this study, the northward jump of the aforementioned systems occurred earlier and the position of the westerly jet shifted from 34–35°N to 38–40°N, which is much further north than its position under typical climatic circumstances. From late May to early June, the subtropical high was extraordinarily powerful, the ridgeline reached 20°N, and its position was further to the north. In years with a late Meiyu onset, the position of the westerly jet and the ridgeline were further south than the climatological average from early to late June; the jump to the north was not evident until late June. In addition, SST anomalies of the Indian Ocean and Pacific Ocean are significant external forcing variables that influence the Meiyu start date. The high SST of the equatorial Indian Ocean and the equatorial tropical eastern Pacific in the autumn of the preceding year and the high SST of the equatorial Indian Ocean in the spring of that year are prophase indicators of an early Meiyu start in the Yangtze-Huaihe River Basin.

An unusual Northwest–Southeast oriented Meiyu rain belt in 2021

Affected by the East Asian summer monsoon, summer floods occur frequently in eastern China, causing huge economic losses and social impacts. In 2021, the precipitation anomaly during the Meiyu period in Yangtze-Huaihe River Valley (YHRV) was abnormally high, with a value of 188.0 mm, about 1.7 standard deviations above normal. However, it did not cause serious flood disasters. This was mainly due to the existence of two precipitation anomaly centers in YHRV, which shared the impact of the excessive precipitation. These two centers were located at the junction of Anhui Province and Henan Province and the junction of Jiangsu Province, Anhui Province and Jiangxi Province, respectively. And more notably, the 2021 Meiyu precipitation anomalies were distributed in a Northwest-Southeast oriented band that is very rare. During the 2021 Meiyu period, the western Pacific subtropical high (WPSH) weakened and extended westward. An anticyclonic circulation anomaly in the lower troposphere was observed over eastern China, which was found to be related to the quasi-stationary wave trains propagating eastward from Hainan Island to the northwestern Pacific by vorticity budget analysis. And the Rossby wave source term played a critical role. In addition, the tropical Atlantic anomalous warming produced convergence anomaly over the eastern Mediterranean and excited quasi-stationary wave trains propagating downstream at the mid-latitudes in upper layers through a monsoon-desert-like teleconnection. It raised the geopotential height over eastern China and thus favored the westward extension of WPSH. These large-scale circulation anomalies generated the anomalous easterly winds along the eastern coast of China and the anomalous southwesterly winds from Guangxi Province to the middle and lower reaches of the Yangtze River. Similar features can be found in the anomalous water vapor transport and the water vapor converged in the YHRV. The above-mentioned reasons jointly caused the abnormally high precipitation anomaly and its unusual pattern in the 2021 Meiyu season. This study might provide a scientific basis and clues for understanding Meiyu precipitation anomalies and disaster prevention and mitigation.